Pokeweed antiviral protein (PAP) is a 29-kDa naturally occurring antiviral agent that can be isolated from the leaves of the pokeweed plant, Phytolacca americana. PAP has a unique ability to depurinate HIV-I RNA. PAP exhibits potent antiviral activity against drug-resistant primary clinical HIV-1 isolates. Both zidovudine (ZDV)-sensitive and ZDV-resistant clinical HIV- 1 isolates were found to be > 4 log more sensitive to PAP than to ZDV. We have cloned the gene for PAP and established procedures for large-scale production and purification of the cloned recombinant pokeweed antiviral protein. We have tested recombinant PAP against a broad panel of viruses in vitro and documented that it is as active as native PAP against both DNA and RNA viruses. We were also able to determine the X-ray crystal structure of pokeweed antiviral protein at 2.1A resolution. More recently, we have used a molecular model of PAP-HIV RNA interactions for the rational design of PAP mutants with potent anti-HIV activity. Two such recombinant PAP proteins, FLP- 102 (151AA 152) and FLP- 105 (191AA 192) have been engineered, produced, and tested both in vitro as well as in vivo. These proteins depurinate HIV-1 RNA much better than ribosomal RNA and are more potent anti-HIV agents than native PAP or recombinant wild-type PAP. Our preliminary studies indicate that the rationally engineered FLP-102 exhibits potent in vivo anti-HIV activity against a genotypically and phenotypically NRTI-resistant clinical HIV-1 isolate in a surrogate Hu-PBL-SCID mouse model of human AIDS. We hypothesize that FLP-102, because of its potent in vitro and in vivo anti-HIV activity may provide the basis for effective salvage therapies for patients harboring highly drug-resistant strains of HIV-1. The goal of this Phase I proposal is: (i) to study the broad-spectrum anti-HIV activity of rationally designed recombinant PAP protein FLP-102; and (ii) to study the in vivo toxicity profile and pharmacokinetic and pharmacodynamic features of FLP-102 in mice. The preclinical data on FLP-102 will be essential to further explore the utility of this novel recombinant PAP mutant for Phase II.